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About us

Atma-Sphere music systems, Inc. is a small company in Saint Paul, MN that has been making world-class vacuum tube music amplifiers since 1976.

We are known for our unique approach to circuit design, resulting in multiple patents and the creation of the first, truly reliable Output TransformerLess (OTL) amplifiers. We made the first balanced-line products in the world of high-end audio, including the MP-1, which was the world's first balanced-line preamp.

All of our amps and preamps are hand-crafted and made-to-order according to each customer's needs. All of our components are hand-selected, and often custom-manufactured especially for us, right down to the wire we use.

The resulting products are unique in the world with an unmatched capacity to reproduce music with intrinsic reliability. 

The Absolute Sound interviews Ralph Karsten

Atma Sphere logo

The reputation of Atma Sphere

Our key achivements in few words


What is Atma-Sphere Music Systems, Inc. all about?

Atma-Sphere was founded in 1978 and is the oldest manufacturer consistently producing OTL (Output TransformerLess) and triode amplifiers. Ralph Karsten designed and patented the music producing circuit which makes our products the best in the world.


Atma-Sphere's claims to fame

The world's first reliable and practical OTL
The world's first fully balanced OTL
The first all triode fully differential zero feedback tube amplifier
The first commercial tube amplifier with only one stage of gain
The most powerful OTL made (the MA-3, producing over 500 watts into 3 ohms)


We also make world class preamps

The world's first fully differential zero feedback all-tube preamp
The world's first all-tube preamp with a direct-coupled balanced output
The world's first and still one of the very few preamps to support the balanced standard (AES48)

Prix et Awards
Ralph Karsten

Ralph Karsten
Founder & Owner

Ralph Karsten is renown for taking the lead in the world of OTL amplifiers, verified by the fact that only three patents have been issued since the 1950s and two of those were to Atma-Sphere. They have also been the first to lead the way when it comes to preamps and were the first manufacturer to produce an all-tube preamp with a direct coupled balanced output.

Connoisseurs of fine music savour the experience provided by components designed by a master of supreme sound. With over 40 years experience in the audio industry focusing on high end audio, Ralph Karsten is simply the best at what he does.

Vidéo AV Showreports

The owner of Atma Sphere presents our products to "AV Showrooms" on YouTube


Atma Sphere
1742 Selby Avenue
St. Paul, MN 55104


Tel : +1 651-690-2246